Diaphragm pumps are used in many pumping applications, and offer several distinct advantages as compared to rotary and other types of pumps. Diaphragm pumps have good suction lift characteristics, good dry running characteristics, and can be up to 97% efficient. Various types of diaphragm pump work well with air and with highly viscous liquids, and can have good self-priming capabilities. Depending on the design, diaphragm pumps can also minimize the number of moving parts that are in contact with the process fluid. This can be ideal for applications to gritty and/or highly viscous liquids, and to corrosive liquids and gases.
FIGS. 1A-1C are highly simplified cross-sectional drawings that illustrate the basic components included in virtually all diaphragm pumps of the prior art. The pump shown in the figures includes a pump housing 118 that surrounds a pumping chamber 100 having a fluid inlet 102 and a fluid outlet 104. The pumping chamber 100 is bounded on one side by a flexible diaphragm 106, which can be distorted so as to increase and/or decrease the volume of the pumping chamber 100. Inlet and outlet valves 108, 110 control the flow of process fluid, so that when the volume of the pumping chamber 100 is increased, as shown in FIG. 1A, process fluid is drawn into the pumping chamber 100 through the fluid inlet 102 and through the inlet valve 108, and when the volume of the pumping chamber 100 is decreased, as shown in FIG. 1B, process fluid flows out of the pumping chamber 100 through the outlet valve and into the outlet.
In some applications, there is a risk that a diaphragm pump may continue to operate when the outlet 110 is blocked, due for example to a clog or to inadvertent closing of an outlet valve. This can cause the pressure in the pumping chamber 100 and outlet 104 to rise to dangerous levels, which could lead to rupture of the diaphragm and/or damage to other components. Spilling of toxic process fluid could also result. Accordingly, many diaphragm pumps include a bypass valve 112 that remains closed during normal operation, but opens to allow fluid to flow from the relatively higher pressure outlet 104 to the lower pressure inlet 102 if the pressure difference rises above a preset threshold value. Typically, the bypass valve is held shut by a bypass spring 114, and the tension of the bypass spring determines the threshold pressure difference that will cause the bypass valve 112 to open. FIG. 1C illustrates flow of process fluid when the outlet 104 is blocked and the bypass valve is open, allowing fluid to flow from the pumping chamber 100 into the outlet 104, through the bypass valve 112 and back into the inlet 102
Of course, the base of the bypass spring 114 must be supported by something. In the simplified example of FIGS. 1A-1C, the bypass valve and spring are installed through an opening in the bypass housing, which is then sealed by a plug 116 that supports the base of the bypass spring 114. However, this can be an undesirable solution, because the bypass plug provides an added opportunity for the system to leak. Another approach is to fasten a bracket to the inner walls within the pump housing to support the spring, but this can add complexity and cost to the design.
It is also frequently desirable to maximize the size of the diaphragm 106 and/or pumping chamber 100, while minimizing the outer volume and weight of the pump. One approach is to make the walls of the pump housing 108 thinner, but this approach is limited because the pump housing must have sufficient strength to withstand the mechanical forces that are applied to it by fluid pressures and flow, and by the mechanical manipulation of the diaphragm. It can be especially difficult to make the walls thinner when the outlet 104 is perpendicular to the input 102, as compared to being in-line with the input 102 as shown in FIGS. 1A-1C.
What is needed, therefore, is a diaphragm pump having a maximized interior pumping chamber volume and a minimized outer size and weight, where the diaphragm pump includes a bypass valve that is easy to install and does not require support by a special plug or mounting bracket.